## -iii- Time

### Measuring Time.

• Very long period of times as years, months, weeks, and days can be counted easily.
• Very short times “fractions of seconds” can be calculated by measuring time for a certain number of pulses, or movements, and then divide this time by the number of pulses.

Tools used

a)   Stop clock

b)   Stopwatch

Tip: Calculation of a period or very short period of time

For measuring short intervals of time (when each period is the same), multiple measurements can be taken and then averaged

e.g. Period of a pendulum  = Time for 10 oscillations / 10

Measure the time needed for n complete swings in T seconds

Periodic time = T/n

Example- 30 swings in 60 seconds

Time of one swing=60 s/ 30 swings = 2 seconds.

Notes:

a)   Time of one complete swing is measured when the string starts its motion from one end and returns back to the same starting point.

b)   Remember there is always a reaction time associated with using a clock or stopwatch

c)   To obtain an accurate record (result) you have to repeat the experiment several times and calculate the average value of your results.

d)   If the length of the string is changed, the periodic time will be also changed, as length of pendulum string increases, its periodic time increases.